Physiological and nutritional responses byLactuca SativaL. to nitrogen sources and mycorrhizal fungi under drought conditions

摘要

We measured the growth, nutrition, and N assimilation of arbuscular-mycorrhizal and non-mycorrhizal lettuce (Lactuca sativaL.) as affected by forms of N and drought. Moisture was maintained at 80 water-holding capacity, and N was applied as NOinf3sup-, NHinf4sup+, or NOinf3sup-/NHinf4sup+(3:1, 1:1, or 1:3). The growth ofGlomus fasciculatum-colonized plants was comparable to that of uncolonized P-supplemented plants when N was provided as NHinf4sup+or combined NOinf3sup-/NHinf4sup+. When N was supplied solely as NOinf3sup-,G. fasciculatum-colonized plants produced a higher yield than P-fertilized plants, suggesting that the uptake and/or assimilation of NOinf3sup-was particularly affected by mycorrhizal status in this water-limited situation. Nutrient availability, except Ca, was less limited for mycorrhizal plants than for P-fertilized plants. P fertilization increased the growth, glutamine synthetase activity, and protein content of lettuce to the same extent thatG. fasciculatumcolonization did when N was applied as NHinf4sup+. With NOinf3sup--fertilization,G. fasciculatum-colonized plants showed increased growth, nitrate reductase activity, and protein content compared to P-fertilizer treatment. Plants colonized byG. mosseaeshowed increased photosynthetic activity and proline acumulation, and these mechanisms may be important in adaptation by the plant to drought conditions. The present results confirmed that under drought conditions, the uptake or metabolism of N forms is particularly affected in mycorrhizal fungi-colonized plants, depending on the mycorrhizal endophyte and the N source added. Thus the significance of arbuscular-mycorrhizal fungus selection for plant growth in drought conditions is a consideration for management strategy.